3GPP Long Term Evolution (LTE) is a standard for mobile phone network technology. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS), and is a technology for realizing high-speed packet-based communication that can reach high data rates on both downlink and uplink channels. As illustrated in FIG. 1, LTE transmissions are sent from base stations 102, such as Node Bs (NBs) and evolved Node Bs (eNBs) in a telecommunication network 106, to mobile stations 104 (e.g., user equipment (UE)). Examples of wireless UE communication devices include mobile telephones, personal digital assistants, electronic readers, portable electronic tablets, personal computers, and laptop computers.
The LTE standard is primarily based on Orthogonal Frequency Division Multiplexing (OFDM) in the downlink, which splits the signal into multiple parallel sub-carriers in frequency, and Single Carrier Frequency Domain Multiple Access (SC-FDMA) in the uplink. A transmit time interval (TTI) is the basic logical unit. A radio resource element (RE) is the smallest addressable location within a TTI, corresponding to a certain time location and a certain frequency location. For instance, as illustrated in FIG. 2, a sub-frame 200 comprised of REs 202 may be transmitted in a TTI in accordance with the LTE standard, and may comprise sub-carriers 204 in the frequency domain. In the time domain, the sub-frame may be divided into a number of OFDM (or SC-FDMA) symbols 208. An OFDM (or SC-FDMA) symbol 208 may include a cyclic prefix 206. Thus, the unit of one sub-carrier and one symbol is a resource unit or element 202.
Long Term Evolution (LTE) systems use Orthogonal Frequency Division Multiple access (OFDM) in the downlink to the communication device and DFT-spread OFDM, which is referred to as single-carrier FDMA (SC-FDMA), in the uplink to the base station or node. The basic LTE downlink physical resource can be viewed as a time-frequency grid as illustrated in FIG. 2, where each resource element 202 corresponds to one OFDM subcarrier 204 during one OFDM symbol interval.
In the time domain, LTE downlink transmissions are organized into radio frames 602 of 10 ms, each radio frame comprising ten equally-sized subframes 604 of length Tsubframe=1 ms, as shown in FIG. 6. The resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.
Wireless communication systems may be deployed in a number of configurations, such as Multiple-Input, Multiple-Output (MIMO) radio systems. An exemplary MIMO system including a base station 302, such as an eNB 302, and user equipment 304 is shown in FIG. 3. When a signal is transmitted by the eNB 302 in a downlink, i.e., the link carrying transmissions from the eNB to the UE 304, a sub-frame may be transmitted from multiple antennas 306, 308 and the signal may be received at UE 304, which has one or more antennas. The radio channel distorts the transmitted signals from the multiple antenna ports. UE 304 may use receiver-diversity signal processing schemes to improve performance.
In an LTE system, transmissions intended for a first user are often overheard by a second, unintended user. The second user may utilize overheard data packets in various ways.
Downlink transmissions are dynamically scheduled. I.e., in each subframe 602, the base station transmits control information about which terminals to which data is transmitted and upon which resource blocks the data is transmitted, in the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe 602. A downlink system with 3 OFDM symbols as control is illustrated in FIG. 7, where the control region is shown at 702, exemplary OFDM control signal symbols are shown at 704, and exemplary reference symbols are shown at 706.
LTE uses Hybrid Automatic Repeat Request (HARQ), where, after receiving downlink data in a subframe, the terminal, or communication device, attempts to decode it and reports to the base station whether the decoding was successful (Acknowledgement—ACK) or not (Non-Acknowledgement—NACK). In the event of an unsuccessful decoding attempt, the base station can retransmit the erroneous data.
Uplink control signaling from the terminal to the base station includes of hybrid-ARQ acknowledgements for received downlink data; terminal reports related to the downlink channel conditions, used as assistance for the downlink scheduling; and scheduling requests, indicating that a mobile terminal needs uplink resources for uplink data transmissions.
If the mobile terminal has not been assigned an uplink resource for data transmission, the L1/L2 control information (channel-status reports, hybrid-ARQ acknowledgments, and scheduling requests) is transmitted in uplink resources (resource blocks) specifically assigned for uplink L1/L2 control on Rel-8 Physical Uplink Control Channel (PUCCH). As illustrated in FIG. 8, these resources are located at the edges of the total available cell bandwidth. Each such resource comprises 12 “subcarriers” 802 (one resource block) within each of the two slots 804 of an uplink subframe. In order to provide frequency diversity, these frequency resources are frequency hopping on the slot boundary, i.e. one “resource” includes 12 subcarriers 802 at the upper part of the spectrum within the first slot of a subframe and an equally sized resource at the lower part of the spectrum during the second slot of the subframe or vice versa. If more resources are needed for the uplink L1/L2 control signaling, e.g. in case of very large overall transmission bandwidth supporting a large number of users, additional resource blocks can be assigned next to the previously assigned resource blocks.
The reasons for locating the PUCCH resources at the edges of the overall available spectrum are two-fold. Together with the frequency hopping described above, this maximizes the frequency diversity experienced by the control signaling. Assigning uplink resources for the PUCCH at other positions within the spectrum, i.e. not at the edges, would fragment the uplink spectrum, making it impossible to assign very wide transmission bandwidths to a single mobile terminal and still retain the single-carrier property of the uplink transmission.
The bandwidth of one resource block during one subframe is too large for the control signaling needs of a single terminal. Therefore, to efficiently exploit the resources set aside for control signaling, multiple terminals can share the same resource block. This can be accomplished by assigning the different terminals different orthogonal phase rotations of a cell-specific length-12 frequency-domain sequence and/or different orthogonal time-domain covers covering the subframes within a slot or subframe.
When carrier aggregation is used in LTE, one uplink carrier is designed to carry the HARQ-ACK/NACK (A/N) bits for all DL carrier Physical Downlink Shared Channel (PDSCH) transmissions. To enable the possibility to transmit more than four bits of A/N, PUCCH format 3 can be used, as disclosed in 3GPP TS 36.211. The basis for Format 3 is DFT-precoded OFDM, as shown in FIG. 9. There are ten SC-FDMA symbols for carrying data and four SC-FDMA symbols for carrying reference signals (RS).
If the number of ACK/NACK bits is up to eleven, then the multiple ACK/NACK bits (which may also include scheduling request (SR) bits) are Reed-Müller (RM) encoded to form 48 coded bits. The coded bits are then scrambled with cell-specific sequences. 24 bits are transmitted within the first slot and the other 24 bits are transmitted within the second slot. The 24 bits per slot are converted into twelve Quadrature Phase-Shift Keying (QPSK) symbols, spread across five DFTS-OFDM symbols using an Orthogonal Cover Code (OCC), applied with cyclic shifts (CS), DFT precoded and transmitted within one resource blocks (bandwidth) and five DFTS-OFDM symbols (time). The spreading sequence is user equipment (UE)-specific and enables multiplexing of up to five users within the same resource blocks.
For the reference signals cyclic shifted, Constant Amplitude Zero Auto Correlation (CAZAC) sequences, e.g. the computer optimized sequences disclosed in 3GPP TS 36.211, are used. To improve orthogonality among reference signals even further, an orthogonal cover code of length two can be applied to the reference signals, but this is not used in LTE Rel. 10. If the number of ACK/NACK bits exceeds eleven, then the bits are split into two parts and two RM encoders are used, one for each part respectively, as disclosed in 3GPP TS 36.212. This is known as the dual-RM code. Up to twenty ACK/NACK bits (plus one SR bit) can therefore be supported by PUCCH Format 3. Each encoder in the dual-RM code outputs twenty-four bits, which are converted to six QPSK symbols per slot. The two sets of six QPSK symbols are interleaved over the subcarriers so that the first encoder maps its six symbols onto odd subcarriers and the second encoder onto even subcarriers. These twelve QPSK symbols are then spread across the five DFTS-OFDM symbols using one out of five orthogonal cover codes, as in the single-RM code case.
Details of the encoding and multiplexing are shown in FIGS. 10(a) and 10(b), where the following algorithm is used in the Dual Codeword Combiner 1016 operation in which {tilde over (b)}0, {tilde over (b)}1, {tilde over (b)}2, . . . , {tilde over (b)}23 is the output sequence from the first encoder 1012; and {tilde over ({tilde over (b)}0, {tilde over ({tilde over (b)}1, {tilde over ({tilde over (b)}2, . . . , {tilde over ({tilde over (b)}23 is the output sequence from the second encoder 1210, where NscRB=12, the number of subcarriers per resource block.
The output bit sequence b0, b1, b2, . . . , bB−1 where B=4·NscRB is obtained by the alternate concatenation of the bit sequences {tilde over (b)}0, {tilde over (b)}1, {tilde over (b)}2, . . . , {tilde over (b)}23 and {tilde over ({tilde over (b)}0, {tilde over ({tilde over (b)}1, {tilde over ({tilde over (b)}2, . . . , {tilde over ({tilde over (b)}23 as follows:
Set i, j=0
while i<4·NscRB                 bi={tilde over (b)}j, bi+1={tilde over (b)}j+1         
bi+2={tilde over ({tilde over (b)}j, bi+3={tilde over ({tilde over (b)}1+1                 i=i+4        j=j+2        
end while
FIG. 10(a) is a flow chart illustrating the details of encoding and multiplexing up to eleven UCI bits. FIG. 10(b) shows the process for encoding and multiplexing from twelve to twenty-one UCI bits in Rel-10. It should be noted that in the “map to . . . ” operation in FIGS. 10(a), 10(b), and 11, a cell, slot, and symbol-specific cyclic shift of the symbols in time domain is included to provide inter-cell interference randomization. Additional details are set forth in the LTE standard specification, 3GPP TS 36.211.
In Rel-10, multiple transmit antennas for the UE were introduced to LTE. For the uplink data channels, multiple transmit antennas allow transmission schemes achieving enhanced reliability in the form of transmit diversity coding or enhanced user data rates in the form of spatial multiplexing. In Rel-10, a transmit diversity referred to as the Space Orthogonal Transmit Diversity (SORTD) was introduced for the PUCCH Format 3. Under the SORTD scheme, the same PUCCH Format 3 signal is transmitted by the UE on multiple transmit antenna ports using different PUCCH Format 3 resources (with different OCC on the coded QPSK symbols and different cyclic shifts for the reference symbols). An improved transmit diversity design based on frequency switched transmit diversity was under investigation for PUCCH Format 3 in Rel-11. The advantage of the frequency switched transmit diversity is that only one PUCCH Format 3 resource (one OCC on the coded QPSK symbols and one cyclic shift for the reference symbols) is consumed even for multiple transmit antenna ports.
FIG. 11(a) is a flow chart illustrating the details of encoding and multiplexing of the frequency switched transmit diversity scheme for up to eleven UCI bits, and FIG. 11(b) is a flow chart illustrating those for twelve to twenty-two UCI bits. The frequency switched transmit diversity for the PUCCH Format 3 is designed to transmit the coded QPSK symbols on different antenna ports using nonoverlapping subcarriers. For the exemplary cases of two transmit antenna ports illustrated in FIGS. 11(a) and 11(b), coded QPSK symbols to be transmitted on antenna port 0 occupy only the even-indexed subcarriers, and those to be transmitted on antenna port 1 occupy only the even-indexed subcarriers.
For signals of simple structures, standard solutions based on Minimum Mean Square Error (MMSE) principles can be applied to suppress the interfering signals. However, for frequency switched transmit diversity coding, such as, for example, the PUCCH Format 3 with frequency-switched transmit diversity coding, standard MMSE solutions cannot achieve proper suppression of interfering signals.
Based on the parameters provided below, the nR×nR interference covariance matrix according to a standard receiver algorithm has been estimated as
                                          M            ^                    s                =                                  ⁢                              1            24                    ⁢                                          ⁢                                    ∑                              k                =                0                            1                        ⁢                                          ∑                                  i                  =                  0                                11                            ⁢                                                          ⁢                              [                                                      r                    ⁡                                          (                                              i                        ,                        k                                            )                                                        -                                                                                    s                        0                                            ⁡                                              (                                                  i                          ,                          k                                                )                                                              ⁢                                                                  h                        ^                                            0                                                        -                                                                                        EQ        ⁢                                  ⁢        1                                                                                                                ⁢                                                                    s                    1                                    ⁡                                      (                                          i                      ,                      k                                        )                                                  ⁢                                                      h                    ^                                    1                                            ]                        ⁡                          [                                                r                  ⁡                                      (                                          i                      ,                      k                                        )                                                  -                                                                            s                      0                                        ⁡                                          (                                              i                        ,                        k                                            )                                                        ⁢                                                            h                      ^                                        0                                                  -                                                                            s                      1                                        ⁡                                          (                                              i                        ,                        k                                            )                                                        ⁢                                                            h                      ^                                        1                                                              ]                                H                ,                                        where xH denotes the conjugate transpose of the vector x. This result can be then combined with estimated channel vectors to form the combining weight vectors:wp=(ĥpĥpH+{circumflex over (M)}s)−1ĥp,  EQ 2:For p=0 and 1.
The main components of interference covariance matrix estimate have been expressed as:{circumflex over (M)}s≈g0g0H+g1g1H+Λ,  EQ 3:where gp is the channel from the pth antenna of the inter-cell interfering UE. Hence, this covariance matrix estimate contains interference powers from both transmit antennas of the interfering UE device. However, each data signal received from the desired UE device is interfered by signals originated from only one transmit antenna of the interfering UE device. Therefore, the combining weight shown in EQ 2 does not match to the received data signal structure. Applying such mismatched combining weight vectors in the receiver leads to inferior reception performance.
Accordingly, there is a need to suppress interference that may be caused by signals from, for example, inter-cell UE devices and intra-cell UE devices in communication networks, for example, using frequency switched transmit diversity coding.